Integrated circuits have been designed to ever-smaller geometries, and required to carry signals of ever-increasing frequencies. As integrated circuit components and signal lines are placed more closely together, and as the frequencies at which the components and signal lines operate are increased to radio frequencies (RF), the components and signal lines strongly couple electromagnetically to the substrate. This results in low power efficiency and restricts the maximum frequency at which the integrated circuit can function.
Previous methods have attempted to overcome the problem of coupling by increasing space between radiant components and receptive components, which results in larger die area and increased production costs. Other previous techniques have boosted the voltage levels of low voltage signals requiring a high degree of isolation; resulting in lower power efficiency and relatively high power emissions that may couple undesirably with other signals.
Previous designs have used trenches to isolate components from a substrate; but such attempts typically fail to yield the 100 decibels (dB) of isolation necessary to integrate systems comprising mixed signal devices (such as base band, phase-locked-loop, or voltage controlled oscillators) or functionally distinct circuits requiring different power levels (such as transmitter or receiver) on the same substrate.
Even with removing or changing the substrate, or isolating the component from the substrate, the degrees of isolation necessary to integrate many RF systems on a single chip have not been achieved. Thus, commercially viable isolation of RF components from the substrate is now needed.